Mapping Potential Groundwater‐Dependent Ecosystems for Sustainable Management

Abstract

Ecosystems which rely on either the surface expression or subsurface presence of groundwater are known as groundwater-dependent ecosystems (GDEs). A comprehensive inventory of GDE locations at an appropriate management scale is a necessary first-step for sustainable management of supporting aquifers; however, this information is unavailable for most areas of concern. To address this gap, this study created a two-step algorithm which analyzed existing geospatial and remote sensing data to identify potential GDEs at both state/province and aquifer/basin scales. At the state/province scale, a geospatial information system (GIS) database was constructed for Texas, including climate, topography, hydrology, and ecology data. From these data, a GDE index was calculated, which combined vegetative and hydrological indicators. The results indicated that central Texas, particularly the Edwards Aquifer region, had highest potential to host GDEs. Next, an aquifer/basin scale remote sensing-based algorithm was created to provide more detailed maps of GDEs in the Edwards Aquifer region. This algorithm used Landsat ETM+ and MODIS images to track the changes of NDVI for each vegetation pixel. The NDVI dynamics were used to identify the vegetation with high potential to use groundwater--such plants remain high NDVI during extended dry periods and also exhibit low seasonal and inter-annual NDVI changes between dry and wet seasons/years. The results indicated that 8% of natural vegetation was very likely using groundwater. Of the potential GDEs identified, 75% were located on shallow soil averaging 45 cm in depth. The dominant GDE species were live oak, ashe juniper, and mesquite.

A Review of Advances in the Identification and Characterization of Groundwater Dependent Ecosystems Using Geospatial Technologies

“…Measurements of leaf water potential, which is rapid and requires just a leaf pressure chamber, can be used to draw conclusions about water availability and compare ecosystems with and without availability to groundwater [10,12,56]. Stable isotope composition of water in the branches of trees is considered to be useful in determining if a given plant is accessing groundwater [56,57]. Moreover, comparison between the stable isotope composition of soil water, surface water, xylem water, and groundwater can confirm the vegetation reliance on the groundwater resource [58][59][60], particularly in semi-arid regions in which groundwater originated from snowmelt or winter precipitation and therefore has a distinctive isotopic composition [61].…”

“…Figure 1 can be used for the selection of remote sensing imagery for GDE detection (from the satellite instrumens that are suitable in terms of spectral and radiometric resolution) considering the cost of acquisition of the image per km 2 [55], the spatial resolution required, and the spatial extent of the studies. Additionally, a review of previous studies in which products from these sensors have been used for identifying the location and extent of GDEs is presented in Table 1 [23,57,81,87,[100][101][102][103][104][105][106][107][108][109], with details regarding the main characteristics (such as spatial resolution and mapping scales) of each sensor and applications that have benefited from and could potentially take advantage of the sensors' capabilities to map GDEs. The approximate mapping scale for which each sensor can be used (Column 3) is based on the spatial resolution of the data.…”

“…This indicator has been used in several studies to identify terrestrial ecosystems and wetlands that depend on groundwater based on the principle that ecosystems that are able to maintain consistent greenness during a prolonged dry period, are defined as potentially groundwater dependent [57,81,107,108]. Other indicators of vegetation density, health, and condition that have been used are the Enhanced Vegetation Index (EVI) and remotely-sensed Leaf Area Index (LAI), as well as indicators of moisture dynamics like the Normalized Difference Wetness Index (NDWI), and tasseled cap (TC) wetness and greenness.…”

Water and forests in the Mediterranean hot climate zone: a review based on a hydraulic interpretation of tree functioning

“…Several models are available to estimate the dynamics of groundwater use by tree transpiration (Gou & Miller, 2014;Orellana et al, 2014;Pinto et al, 2014). The large-scale mapping of zones where roots might have or not access to groundwater (groundwater dependent ecosystems) has been most frequently done indirectly, through remote sensing techniques coupled with geographic information systems (Howard & Merrifield, 2010;Gou et al, 2015;Yin et al, 2015). However, these two technological tools are not yet widely applicable and require further development and validation.…”

A land surface temperature model-data differencing approach to quantifying subsurface water use by vegetation: Application in the Condamine region, south-eastern Queensland

“…There are several different types of methods used to identify GDV in the landscape including satellite remote-sensing techniques (e.g. Barron et al, 2014;Fu and Burgher, 2015;Gou et al, 2015;Lv et al, 2013;Munch and Conrad, 2007;National Water Commission, 2012a;Tweed et al, 2007;van Dijk et al, 2015;Zhou et al, 2013), water table fluctuation methods (e.g. Butler et al, 2007;Loheide et al, 2005); and field-based stable isotope analysis (e.g.…”